Background The study evaluated phytochemical composition, antidiabetic, oral glucose tolerance test and in vitro antioxidant activities of hydromethanol extract of Paullinia pinnata root bark. Methods Cold maceration method was used in extract preparation and scavenging of 2,2-diphenyl-1-picrylhydrazyl radicals was used to evaluate antioxidant properties of the extract. Diabetes was induced with alloxan at the dose of 160 mg/kg. The antidiabetic activity of the extract was tested at doses of 50, 100 and 200 mg/kg, and glibenclamide was used as reference drug. Results Phytochemical analysis of the extract showed the presence of alkaloids, flavonoids, glycosides, tannins, saponins and terpenes/sterols. The extract produced a significant (p<0.05) time-dependent decrease in the fasting blood glucose (FBG) levels in the treated rats when compared with the distilled water treated rats, but did not produce dose-dependent effects. The extract 50, 100 and 200 mg/kg and glibenclamide (2 mg/kg) caused 83.62 %, 60.66 %, 47.77 % and 68.52 % reduction respectively in FBG at 6 h post-treatment while the distilled water (5 mL/kg) produced 8.12 % reduction in FBG at 6 h post treatment. The extract (50 mg/kg) and glibenclamide (2 mg/kg) produced a significant (p<0.05) oral glucose tolerance effect in both normoglycemic and diabetic rats. The extract produced concentration-dependent increase in antioxidant activity and had its optimum effect at 400 µg/mL concentration. Conclusions This study suggests that P. pinnata root bark has potent antidiabetic and antioxidant activities and also validates its use in folkloric medicine in the management of diabetes-related conditions.